Method of preparing reducing gas

ABSTRACT

Reducing gas containing CO and H2 as the major ingredients is prepared by partially oxidizing a hydrocarbon oil with oxygen or oxygen rich air to produce an intermediate gas containing CO2 and H2O and converting CO2and H2O into CO and H2 by means of a gaseous hydrocarbon such as coke oven gas or natural gas by using the heat generated by the partial oxidation. Furnace top gas exhausted from a reducing furnace may be added to the partially oxidizing zone.

United States Patent Miyashita et al.

[ METHOD OF PREPARING REDUCING GAS [75] Inventors: Tsuneo Miyashita;Toshio Nayuki,

both of Kawasaki; Kazuo Sano, Yokohama; Takeo Yamada, Yokohama;Shoichiro Ohzeki, Yokohama; I-Iiroaki Nishio, Kawasaki, all of JapanOct. 14, 1975 [56] References Cited UNITED STATES PATENTS 3,536,45510/1970 von Bogdandy et al 48/107 X 3,813,229 5/l974 Pagani 75/42Primary ExaminerL. Dewayne Rutledge Assistant ExaminerM. J. AndrewsAttorney, Agent, or FirmFlynn & Frishauf 5 7 ABSTRACT Reducing gascontaining CO and H as the major ingredients is prepared by partiallyoxidizing a hydrocarbon oil with oxygen or oxygen rich air to produce anintermediate gas containing CO and H 0 and converting CO2 and H 0 intoCO and H2 by means of a gaseous hydrocarbon such as coke oven gas ornatural gas by using the heat generated by the partial oxidation.Furnace top gas exhausted from a reducing furnace may be added to thepartially oxidizing zone.

5 Claims, 1 Drawing Figure Oil C0: 25% co 36% Hz 40% N: 23%

METHOD OF PREPARING REDUCING GAS BACKGROUND OF THE INVENTION Thisinvention relates to a method of preparing reducing gas and moreparticularly to a method of preparing at high efficiencies reducing gascontaining at least less than 7 of CO and H and only a little quantityof free carbon by partially oxidizing a hydrocarbon while incorporatingthereto oxygen or oxygen rich air. The invention also relates to amethod for preparing at an extremely low cost reducing gas of thecharacter described above by utilizing as the main raw material furnacetop gas exhausted from-the top of a reducing furnace, for example ablast furnace and containing CO and H 0.

By blasting reducing gas into a blast furnace or a shaft furnace it ispossible to reduce the amount of coke which is required to be chargedinto the furnace to act as a reducing agent and hence to increase theamount of the iron ore charged in the furnace thereby improving the O/Cratio as well as the production of the cast iron. Regarding thepreparation of reducing gas utilized for this propose, a member ofmethods have been proposed and practically used. Among these prior artmethods may be mentioned a partial oxidation method wherein ahydrocarbon oil or hydrocarbon gas is caused to react with pure oxygenor oxygen rich air containing more 0 than 75 and a method wherein thegas exhausted from the top of a reducing furnace is modified by naturalgas this preparing reducing gas by heat decomposition. However, theseprior art methods have the following disadvantages. More particularly,in the partial oxidation method, in order to obtain reducing gascontaining small quantities of CO and H O by the partial oxidationreaction it is necessary that the percentage of pure oxygen to beincorporated into the hydrocarbon oil or hydrocarbon gas to a value beremarkably smaller than that required for an ordinary oxidation process.For example, when heavy oil is used as the raw material, unless thequantity of pure oxygen per one kilogram of the carbon contained in theheavy oil is decreased to about from 0.95 to 0.97 Nm, it is impossibleto effect the desired partial oxidation reaction. With such lowpercentage of oxygen it is inevitable to form a large quantity of freecarbon or soot. For this reason, it is necessary to add a quantity ofsteam or the like to act as a moderator soot preventing agent or abuffer Addition of steam increases the quantity of H 0 in the resultingreducing gas and where reducing gas is blown into a blast furnace or ashaft furnace it consumes a large quantity of the reducing agent or cokecharged in the furnace. Although it is possible to alleviate thisdifficulty by increasing the percentage of the pure oxygen, increase inthe percentage of the pure oxygen increases the contents of CO and H 0in the resulting reducing gas thereby impairing the reducing capabilitythereof. The partial oxidation process is so carried out withappropriate compromise between soot content and character of thereducing gas. Although a suitable compromise can be attained by asuitable selection of the quantity of oxygen used, a substantialquantity of soot is inevitable as has been pointed out hereinabove. (atleast more than IOg/Nm? and in an extreme case more than g/Nm Accordingto the heat decompositon process, a hydrocarbon oil or a hydrocarbon gasis merely heat decomposed by the heat accumulated in a heat exchanger sothat it is necessary to accumulate heat in the heat exchanger bysuitable means. The composition of the resulting reducing gas and thecontent of soot contained therein are determined solely depending uponthe quantity of heat accumulated. Moreover, the operation istroublesome, and the composition and the temperature of the reducing gasare not always constant at the start and the end in the making of thegas. It is difficult to adjust the composition.

SUMMARY OF THE INVENTION Accordingly, it is an object of this inventionto improve the method of preparing reducing gas by the partial oxidationprocess so as to produce high quality reducing gas containing a smallquantity of soot regardless of the ratio of oxygen to the raw materialhydrocarbon oil or the hydrocarbon gas. Contrary to the prior art methodof preparing reducing gas wherein the reducing gas is prepared by asingle process step, it is a feature of this invention to use acombination of two process steps. In the first step the hydrocarbon isoxidized by incorporating therewith oxygen or oxygen rich air, whereasin a second step a gaseous hydrocarbon is incorporated into theintermediate gas produced by the first step so as to pyrolyze andimprove the quality of the intermediate gas. This invention is suitableto reform a hydrocarbon by using CO and H 0 in a furnace top gas withpartial oxidation of the oil, as the abovementioned two steps. Accordingto the novel method of this invention it is not necessary to maintain aparicular ratio of oxygen to the raw material hydrocarbon as in theprior art partial oxidation process thereby enabling a desired partialoxidation reaction with a higher oxygen ratio in a wide range, with theresult that the operation is greatly simplified and the formation ofsoot is greatly decreased. With this first step, the quantities of COand H 0 generated increase proportionally with the oxygen and thequantity of heat generated by the partial oxidation reaction alsoincreases. However, the quality of the intermediate gas can be improvedby the second step in which a gaseous hydrocarbon is incorporated andthe resulting mixture is pyrolyzed. More particularly, in the secondstep, CO and H 0 produced in the first step are converted into CO and Hwhich are advantageous for the reducing gas. Moreover, the heatgenerated in the first step is advantageously and reversibly used forthe heat of pyrolysis. With these two steps, even if the composition ofthe intermediate gas resulting from the first step is not constant it ispossible to adjust or improve the composition by the second step therebymaking it possible to produce reducing gases of any desired compositionor characteristic. Thus it is always possible to assure stable operationand to reduce the quantity of soot. Moreover, it is not necessary toprepare any source of heat necessary for the pyrolysis and improvementof the quality of the reducing gas.

Another object of this invention is to obtain reducing gas at a lowcost. As has been pointed out hereinabove, since the method of thisinvention is easy to carry out and since it is not necessary to installany independent source of heat for the pyrolysis it is possible togreatly reduce the cost of manufacturing the reducing gas. Moreover, inaccordance with the method of this invention exhaust gas exhausted froma reducing furnace such as a blast furnace and containing appropriatequantities of CO and H 0 is used as the principal raw material. It ispossible to reduce the cost of manufacturing reducing gas by at leastmore than 30 than the prior art methods described above. Usually, it ispossible to reduce the cost by even more.

BRIEF DESCRIPTION OF THE DRAWING Further objects and advantages of theinvention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawing in whicha single FIGURE is a diagrammatic representation for explaining theprocess steps of the method of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the accompanyingdrawing furnace top gas 2 exhausted from the top of a reducing furnace 1such as a blast furnace and containing CO. and H 0, is admitted into theheating section 4 of a gas manufacturing furnace 10 via dehydrating anddust removing device 3. In the furnace 10 are installed oxy-fuel burners5 and 6 to atomize a hydrocarbon oil. Oxgen or oxygen rich air isadmixed with the atomized hydrocarbon oil at a ratio in a rangedescribed above to effect a partial oxidation combustion or the firstprocess step to form hydrocarbon gas which is mixed with the furnace topgas to act as the modifying gas. Furthermore, hydrocarbon gas such ascoke oven gas 11 HQ 45 55 %,CH,,35 -45% ,CO:3-6%,CmHn:2-4%) is admixedwith said gas mixture in a reformer thereby effecting the pyrolysis ofthe second process step. More particularly, reducing gas of the desiredquality is produced from a hydrocarbon oil without forming soot bysupplementing by itself the heat required for the pyrolysis and byadjusting the atmosphere at the time of switching. The resultingreducing gas is admitted into the blast furnace 1 via a conduit 12. Thegas is blown into the furnace through an inlet part 13 provided abovethe tuyers not shown. Thus, the reducing gas manufacturing furnace ofthis invention is combined with the blast furnace l to effect partialoxidation of the top gas exhausted from the blast furnace and theresulting reducing gas is blown into and circulated through the blastfurnace. This arrangement reduces not only the quantity of the discardedgas but also the heat loss, thereby assuring efficient operations bothin the blast furnace l and the reducing gas manufacturing furnace l0. 1

The principle of operation of the method of this invention capable ofbeing carried out by the arrangement described above is as follows Thepartial oxidation of a hydrocarbon ofa hydrocarbon oil can be expressedby the following equation (I).

in which CmHn represents heavy oil, for example, and corresponds to avalue of about 0.95 to 0.97 Nm /Kg/(C) as in the prior art method. Thevalue a amounts to from 2 to 6 by volume based on the total quantity ofthe gas produced, [2 equals to -45 d equals to l8-60%, and e equals tofrom 4 to 18 The value a represents the quantity of heat generated andin the partial oxidation process is used to increase the temperature ofthe resulting reducing gas. Of course this heat quantitiy is equal tothe difference between the sum of the heat quantities generated by theformation of CO CO and H 0, and the heat of pyrolysis of CmHn, and theseheat quantities per mole have the values as shown by the followingequations ll to lV C 0 CO 97.2 Kcal/mol l1 C V20 C0 29.6 Kcal/mol in HA20 H O 57.8 Kcal/mol lV As can be noted from these equations, the heatsof forming CO and H 0 are much larger than that of CO expressed byequation lI l This means that increase in the value ofa in equation lcauses a large quantity of O to react thus increasing the quantities ofCO and H 0. This also increases the quantity of heat q, generated as canbe clearly understood from equations ll and IV It is also possible todecrease the quantity of soot shown by [and c in equation I byincreasing a If a is increased to a value corresponding to about 2.6 to3.0 Nm"/Kg/(C), j' and 0 become substantially zero. Considering thecharacteristic of the reducing gas, although it is possible to reducethe quantity of soot jlc by increasing the value of a the quantities ofCO and H 0 are also increased which is of course undesirable. For thisreason, it is advantageous to limit the sum of CO and H O'in theresulting reducing gas not to exceed 10 even though a small quantity ofsoot may be formed. To this end, the value of a should correspond toabout 0.95 to 0.97 Nm /Kg/(C). According to this invention, however, theCO and H 0 components formed in a reducing furnaceare decomposed by thehydrocarbon gas Cm'Hn as shown by the following equation V Thus, thereaction process according to equation V to form reducing gas consistingessentially of C0 H is endothermic so that it is necessary to supplementa heat quantity q.

From the foregoing description it can be noted that the invention ischaracterized in that a hydrocarbon oil is partially burnt according toequation I with a value ofa selected in a range not to form as far aspossible soot and to form gas containing excess a quantities of CO and H0. Thereafter an excess quantity of a gaseous hydrocarbon CmHn is addedto the gas for converting the CO and H 0 into CO and H and a portion ofthe heat q, generated by the reaction of equation I is used reversiblyas the heat for converting CO and H 0 into CO and H In other words,chemical reactions expressed by the following equation l) and Vl proceedin parallel.

when qc represents the heat of forming uCO and eH- O uCO eH O Cm'Hn qt-(a+m')CO (e+n'/2)H vl) As can be noted from an equation of equilibriumof water gas reaction, although all of the CO and H 0 are not alwaysconverted into CO and H according to this invention it is possible toselect the value of a to have a value of 1.30 or more which is extremelylarger than that utilized in the conventional partial oxidation process.Consequently the value of a amounts to from 7 to 10 by volume based onthe total volume of the gas c oil co 97.2 Kcal/mol Co CH 2C0 2H 59.1Kcal/mol Vll Vlll Adding equations V11 and VIII C oil 0 CH 2C0 2H 38.1KCal/mol (IX) As can be noted from these equations, since the heat ofreaction is used reversibly it is not necessary to supplement heat fromoutside. Even when the percentage of the reducing gas formed by thepartial oxidation of the hydrocarbon expressed by equations I and 1X issmall with respect to the total volume of the gas there is no problem.

Referring again to the accompanying drawing, after dehydration and dustremoval, the furnace top gas 2 exhausted from reducing furnace l orblast furnace has a composition of l8-22 of CO 2-50 of H and 8-57 of Nfor example. After heating in the heating section 4, the gas is admittedinto the reducing gas manufacturing furnace l0 equipped with oxyfuelburners 5 and 6. The gas is then partially burnt by selecting a ratio O/oil of 1.30 Nm/Kg/(C), for example, to produce intermediate containinghigher contents of CO; and H 0 than the conventional method. Theintermediate gas thus produced is then caused to react in the re- CO andH O H The resulting reducing gas generally has a composition of 2-4 ofCO 30-40 of CO, 18-60 of H and 4-36 of N all in volume percent, and canbe directly blown into the reducing furnace l.

The same can also be obtained by incorporating a gaseous hydrocarboninto a partially oxidized hydrocarbon oil and then converting themixture in the manner described above. in this case, since the gas ex-10 hausted from the top of a reducing furnace is not used,

the hydrocarbon oil is partially oxidized by the oxy-fuel burners 5 and6 in the furnace l0 and the CO and H 0 components contained in theresulting intermediate gas are pyrolyzed and converted in into CO and Hin the reformer 8 by a gaseous hydrocarbon such as coke oven gas ornatural gas.

In each case, the value of O contained in the oxyfuel used to partiallyoxidize the hydrocarbon oil should be in a range of from 1.00 to 3.00 NmlKg/(C).

If this value decreases below 1.00 the quantity of soot formed increasesthereby imparing the quality of the resulting reducing gas. On thecontrary, when the value of oxygen exceeds 3.00, although the quantityof soot can be reduced to an extremely small value the result would bethe same as if the hydrocarbon oil were burnt completely, thusincreasing the quantity of CO so that by converting this CO by gaseoushydrocarbon it is im possible to produce valuable reducing gas.

Seven examples of this invention are shown in the following tabletogether with two control example. The

composition of the blast furnace gas utilized in these examples was: CO18 CO, 23 H 2 and N 57 and the composition of the heavy oil was C,90.5%; Specific Gravity 20(A.P.l.), Pour Point 6 C.

The coke oven gas had a composition of CH 30 CmHn, 3 CO, 6 and H 55Control Control Ex. 1 Ex. 2 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7

Raw material Blast furnace gas Nm' /hr. 220 220 220 220 220 220 Cokeoven gas Nm lhr. 128 128 128 128 114 148 132 134 Heavy oil Kg/hr. 20 8420 20 20 40 40 20 20 Oxygen 1 Nm /hr. 16 67 20 22 26 52 58 33 48 Oz/C inoil Nm lkg 0.95 0.92 1.17 1.29 1.52 1.51 1.70 1.96 2.86 Reducing gasTemp. of reducing gas C 1000 1000 1000 990 990 1010 1060 1010 1000 CO(30.6 48.7 34.3 33.7 33.9 45.5 42.2 30.2 27.4 CO 2.1 3.6 2.4 2.7 3.2 2.52.8 5.2 7.8 H 41.1 42.1 41.4 41.2 41.4 49.6 52.3 40.5 41.1 CH, tr. tr.tr. tr. tr. tr tr. tr. tr. Soot formed g/Nm 18.3 19.8 6 1 4.8 2.6 1 61.5 1.5 1.3

former 8 with the CH and CmHn components of coke oven gas having acomposition as shown in the drawing and preheated to a suitabletemperature by heating furnace 7 thereby converting CO and H 0 in theintermediate gas into reducing gases CO and H The heat quantities formedby the reactions C CO and H H O are used for the endothermic reactionsCO As can be noted from this table the quantity of the soot formeddiffers greatly between the control examples wherein the quantities of Oin Oz/(C in oil) are 0.95 and 0.92 Nm /Kg and the examples of thisinvention wherein the quantities of O exceed 1.0 Nm /Kg. Especially inexamples 4 to 7 the quantity of soot formed is below 2.0g/Nm Test wasalso made wherein the value of O in O- /(C in oil) was selected to behigher than 3.00. In this case, the quantity of- CO generated in thefirst step was from 8 to 20% and that of H was from 16 to 40 In order topyrolyze the intermediate gas containing such amounts of CO and H 0 itwas necessary to use a greater quantity of coke oven gas of the order of300 Nm-lhr than the case shown in example 7.

From the forgoing description it can be noted that the inventionprovides a novel method of preparing reducing gas without regard to theratio of oxygen to fuel which is the most important factor in the methodof manufacturing reducing gas by partial oxidation process, thus makingit possible to produce valuable reducing gas by selectingthe ration ofhigher than unity and to greatly decrease the quantity of soot formed.Moreover, according to this invention, the intermediate gas is convertedby a gaseous hydrocarbon to obtain reducing gas having excellentcomposition and characteristic and can be advantageously used in suchreducing furnaces as a blast furnace. Furthermore, the partial oxidationreaction which is inherently an endothermic reaction is caused toproceed in parallel with the conversion of the furnace top gas byhydrocarbon gas thus making it possible to use furnace top gas as themain raw material. Thus, the heat of reaction is efficiently utilized tocontrol the composition and temperature of the reducing gas formed sothat it is possible to prepare valuable reducing gas at an extremely lowcost.

Although the invention has been described in terms of particularexamples thereof it should be understood that many changes andmodifications will be obvious to one skilled in the art withoutdeparting from the true spirit and scope of the invention as defined inthe appended claims. What is claimed is:

1. A method of preparing reducing gas comprising the steps of Ipartially oxidizing a hydrocarbon with oxygen or oxygen-rich air to forman intermediate gaseous product containing CO and H 0, wherein heat isgenerated, the quantity of oxygen being from 1 to 3 Nm/Kg of carboncontained in said hydrocarbon, and pyrolyzing said intermediate gaseousproduct and a gaseous hydrocarbon with said heat whereby said CO and H 0are converted into a reducing gas containing CO and 2. The methodaccording to claim' 1 wherein said hydrocarbon is a hydrocarbon oil andsaid gaseous hydrocarbon is coke oven gas or natural gas.

3. A method of preparing reducing gas comprising the steps of atomizingand partially oxidizing a hydrocarbon oil with oxygen or oxygenrich air,wherein heat is generated, the quantity of oxygen being froml to 3 Nm/Kgof carbon contained in said hydrocarbon oil, admixing the resulting gaswith a furnace top gas exhausted from a reducing furnace to form anintermediate gas containing CO and H 0 and incorporating a coke oven gasor a natural gas with said intermediate gas and pyrolying the resultingmixture with said heat, whereby said CO and H 0 are converted into areducing gas containing CO and H 4. The method according to claim 3wherein said reducing gas is blown into said reducing furnace.

5. The method according to claim 4 wherein said reducingfurnace is ablast furnace.

UNITED STATES PATENT AND TRADEMARK OFFICE Q TEFTQATE 0F ECTIQN PATENTNO. 3,912,502

BATED October 14, 1975 mvmrorus) TSUNEO MIYASHITA et al Q it iscertified that error appears in the ab0ve-identified patent and thatsaid Letters Patent are hereby corrected as shown below;

Column 1, line 23: replace "propose" with purpose Column 1, line 23:replace "member" with number G Column 1, line 30: replace "this" withthus Column 2, line 31: replace "paricular" with particular Q Column 6,line 63, and Column 7, line 7:

replace "O in O /(C in oil) with o /(c in oil) Column 8, line 27, Claim3: replace "pyrolying" with 5 pyrolyzing Column 5, line 2: replace"form" with from a Column 6, line 6: after "same", insert result Signedand Sealed thisthirtieth D f March 1976 [SEAL] Attest:

RUTH C. MASON c. MARSHALL DANN Q Arresting Officer Commissioneruj'Patents and Trademarks

1. A METHOD OF PREPARING REDUCING GAS COMPRISING THE TEPS OF PARTIALLYOXIDIZING A HYDROCARBON WITH OXYGEN OR OXYGENRICH AIR TO FORM ANINTERMEDIATE GASEOUS PRODUCT CONTAINING CO2 AND H2O WHEREIN HEAT ISGENERATED THE QUANTITY OF OXYGEN BEING FROM 1 TO 3 NM/3KG OF ARBONCONTAINED IN SAID HYDROCARBON AND PYROLYZING SAID INTERMEDIATE GASEOUSPRODUCT AND A GASEOUS HYDROCARBON WITH SAID HEAT WHEREBY SAID CO2 ANDH2O ARE CONVERTED INTO A REDUCING HAS CONTAINING CO AND H2.
 2. Themethod according to claim 1 wherein said hydrocarbon is a hydrocarbonoil and said gaseous hydrocarbon is coke oven gas or natural gas.
 3. Amethod of preparing reducing gas comprising the steps of atomizing andpartially oxidizing a hydrocarbon oil with oxygen or oxygenrich air,wherein heat is generated, the quantity of oxygen being from 1 to 3Nm3/Kg of carbon contained in said hydrocarbon oil, admixing theresulting gas with a furnace top gas exhausted from a reducing furnaceto form an intermediate gas containing CO2 and H2O , and incorporating acoke oven gas or a natural gas with said intermediate gas and pyrolyingthe resulting mixture with said heat, whereby said CO2 and H2O areconverted into a reducing gas containing CO and H2.
 4. The methodaccording to claim 3 wherein said reducing gas is blown into saidreducing furnace.
 5. The method according to claim 4 wherein saidreducing furnace is a blast furnace.